2.1 Networks including the Internet

Router Function and Role

A router is a crucial networking device that forwards data packets between computer networks. It acts like a traffic director for data, determining the best path for information to travel from one network to another. Routers are fundamental to the operation of the internet and large networks.

Core Function: Packet Forwarding

The primary function of a router is to examine the destination address of incoming data packets and then forward them towards their intended destination. This process involves several key steps:

1. Receiving a Packet: The router receives a data packet from one network interface.
2. Examining the Destination Address: The router analyzes the packet's destination IP address.
3. Looking Up the Destination Network: The router consults its routing table to determine the best path to the destination network.
4. Forwarding the Packet: The router forwards the packet to the next hop – another router or the final destination network.

Routing Tables

Routers use routing tables to make forwarding decisions. A routing table is a database that contains information about the networks reachable through each of the router's interfaces. Each entry in the table typically includes:

• Destination Network: The IP address range of the network.
• Next Hop: The IP address of the next router or device to forward the packet to.
• Interface: The interface on the router that should be used to send the packet.
• Metric: A value indicating the cost of using this route (lower metric usually indicates a better route).

Types of Routing

There are different types of routing protocols used by routers:

• Static Routing: Routes are manually configured by a network administrator. Simple to set up but not adaptable to network changes.
• Dynamic Routing: Routers automatically learn routes by exchanging information with other routers. More complex to configure but more adaptable. Examples include RIP, OSPF, and BGP.

Role in the Internet

Routers are the backbone of the internet. They connect networks together, allowing devices on different networks to communicate. Here's how they contribute:

• Connecting Home Networks: Your home router connects your home network to your Internet Service Provider (ISP)'s network.
• Connecting ISPs: Large routers connect different ISPs together, forming the internet backbone.
• Data Path Determination: Routers determine the most efficient path for data to travel across the internet, considering factors like network congestion and link quality.

Feature	Description
Function	Forwards data packets between networks.
Routing Table	Database containing information about reachable networks and the best paths to them.
Routing Protocols	Protocols used to dynamically learn and update routing tables.
Role in Internet	Connects networks, determines data paths, and enables communication across the internet.

Suggested diagram: A diagram showing a network with multiple routers connecting different networks and devices. The diagram should illustrate data packets being forwarded between networks by the routers.